Monday, November 8, 2010

If there is one animal that that can be said to symbolize the mysterious wildness inherent in the deep jungle, it's the panther. The black coats seen in these animals have inspired myths and legends across many cultures throughout the ages. However, such a beast, as an independent entity, does not exist. Instead, these popular animals are in fact black morphs of more commonly known cats. Such coat colorings have been reported in the jaguar of the Americas and, more famously, in the leopard. However, in most areas melanism (the more formal name for such a coloring), a recessive trait in leopards, is a relatively rare occurrence. One remarkable exception can be found in the Malay Peninsula, a thin region of land comprising pieces of both Thailand and Malayasia found just south of the Isthmus of Kra.

Reports of a bounty of melanistic leopards in this area have been found as early as the 19th century. However, a scientific assessment of the status of these creatures is a remarkably difficult process. Leopards are solitary animals and incredibly reclusive by nature. For somebody to so much as catch a glimpse of a leopard is a fantastically rare event. As such, to assess the frequency of color patterns in a broad geographic region, searching for the animals on foot is not an option. Instead, an international team of scientists have opted for a higher-tech option: infrared imaging systems. Strategically placed, these cameras have been proven to be exceptionally useful for capturing images of otherwise elusive wildlife. To determine the frequency of this color pattern, the researchers pooled together data from camera trapping projects in over 22 separate locations throughout the Malay Peninsula and the regions bordering it to the north. Taken together, they recorded some 474 images of leopards over 42,565 collective camera trapping nights. What they found was quite remarkable.

Of the 22 camera trapping sites in the study, 16 captured images of leopards. The melanistic morph was found in all camera trapping sites that recorded leopards, but the spotted morph was only found in those areas north of the Isthmus of Kra. This suggests that though one cannot conclude that spotted leopards are entirely absent with the present dataset (indeed, they have been previously reported in the area), they are rare enough that it's likely that the recessive allele for melanisim is 'nearly fixed' in the population. One possibility that could explain the prevalence of melanistic leopards is through genetic drift, wherein genes are shuffled about the population, and through chance, change in frequency. The authors ran a variety of scenarios, using different population sizes to determine the amount of time required for genetic drift alone to account for the unique status of the Malay leopards. These ranged from 1,100 years with a population of 100 (which would have lead to a severe bottleneck) to 100,000 years with a population of 5,000, with a myriad of scenarios in between.

Therefore, the question remains--to what degree is the frequency of melanism in the leopard population due to genetic drift (which would require a high amount of geographic, and therefore reproductive isolation), and to what degree was the near fixation due to natural selection? Genetic studies of tigers have suggested that gene flow has indeed been very much reduced between the two areas, and as such it seems likely that genetic drift had at least some play in this evolutionary event. Suggested causes for these genetic bottlenecks include the rise of sea levels caused by the end of the last ice age and the volcanic winter that would have occurred when Mount Toba erupted 74,000 years ago. These bottlenecks would have detectible signatures in the genes of the Malay leopards, and future genetic studies will help test for such a possibility. However, there have been selective benefits of melanism postulated, including increased camouflage in densely forested environments. This too may have helped meld the leopard population of the Malay Peninsula.

The authors conclude that "it is likely that both genetic drift and natural selection have been involved at different stages in the history of leopard melanism, providing a unique system for studying the adaptive genetics of carnivore coloration." Surely, many surprises and wonders await in the study of Malay's secretive leopards

Friday, September 17, 2010

Ask a given person to name one of the four big cats, and the lion (Panthera leo) is likely to top the list. They're fierce, large, and remarkably charismatic. Throughout history, lions were integrated into the symbology of many cultures, representing such ideal traits as nobility and courage. And indeed, however much one can say such a thing, these traits can be found in lions at large. But it does no good to anthropomorphize. Lions are living organisms that fight for survival each day. To truly understand the nature of the lion requires biological research, and this research has created a vast and fascinating body of data.

Lions live in what are called 'fission-fusion' societies, in which a group separates and reforms throughout their daily activities. Lion prides comprise 1-22 adult females, their collective offspring, and a coalition of 1-9 males. These males will defend the pride against invading males, while the females will protect their offspring from infanticide by invading males, and intrusions by the females of other prides. Territory quality has been linked to reproductive success and survival, and is therefore key in the overall quality of lion lives. Because of this, when an invasion occurs, one could suggest that it would be overall better for the maximum number of pride members to respond to territorial intrusions. The more lions that respond, the better the chances of driving off a given number of invaders. However, an experiment performed by researchers from the University of Minnesota and the Australian National University suggests that the true nature of lion responses is more complex.

To simulate a territorial threat, researchers recorded the roars of a single female as well as three separate females. These roars were then played through a loud speaker within the territories of eight prides throughout Serengeti National Park and Ngorongoro Crater, Tanzania. To measure the responses of female lions, the researchers recorded the amount of time it took a given lion to reach the midpoint between the speaker and the lions ('latency'), the differences in the times it took each given lion to reach that midpoint (the 'lag time'), the order within the group that each lion reached the midpoint, and the number of backwards glances given by each lion within the group.

They then analyzed these standardized ranks to determine the degree of responsiveness to these intrusions. Some lions were consistently on the ball when a roar was played, immediately adopting an aggressive response while moving towards the playback. However, others were what were dubbed "laggards": lions that are less likely to rush towards the source of the threat. Laggards consistently slowed the approach of more active lions, causing them to pause and look back to verify that the laggard was still approaching.

Response times and actions of lions responding to territorial roars.

Interestingly, not all laggards lagged equally in every situation (though some did). Some were more likely to approach the speaker quickly when there were more invaders (and would therefore be more in need), while others lagged more when there were more invading lions relative to responders (lending an injury more likely).

This study suggests that though logic may dictate immediate responses to a territorial invasion, the responses of lions may vary substantially depending on the situation. Lion society is complex, and the consequences of that complexity are many. This kind of research helps unlock the secrets to lion behavior, and though they may certainly have applications to lion conservation, the more of nature's hidden facets we can uncover the better.

Thursday, September 16, 2010

Sorry about the long break--this summer has been very eventful. Amongst other things, I spent two months working the famous Egg Mountain site with the Museum of the Rockies, submitted (and revised) a review paper on the Spinosauridae, and slightly altered my career trajectory by switching to an Ecology and Evolution major. So, though updates may be periodic, expect updates on life in all its forms, ancient or modern.

In the mean time, here are some pictures of my various adventures.

As we say, tearing it down.

Mountain goats in the Beartooths, a half hour or so outside Egg Mountain.

Sunset just outside our camp. In the distance lie the foothills of the Rockies.

Hiking near my home in eastern Montana.

Your humble author near the falls in Yellowstone National Park.

Turbulence and chaos all.

One of the many ravens native to Yellowstone.

Yellow-bellied marmot.

The famous Lamar Valley, home of the now defunct Druid Peak wolf pack. Though alas, the wolves were with the elk in the high country.

Thursday, May 20, 2010

A hardware store manager, on his day off, visits the local Sea World. While strolling about and enjoying the various sights, he gasps as he sees one of his employees throwing boxes of Swiss Army Knives into one of the pools.

Sunday, May 2, 2010

So, having read that describing a bone is one of the best ways to learn its features well, this is something I wrote up last night. Obviously it's a cast, but it's a very well done cast, so most of the features I describe should be in the real bone.

I'll note that because my access to the kind of literature I need to make any kind of comparative basis is currently limited (at least until the Fall), I've only focused on the features of the claw itself, and not how they relate to other theropod dinosaur groups.

With that said, I'd appreciate any comments/tips you may have!

*****

The element, a robust left manual ungual I missing the distal tip (which is fractured at a point transversely distal from the ventral margin of the articular facet and flexor tubercle), measures 190 mm in a line perpendicular to the articular facet and 305 mm across its convex, recurved dorsal margin.Its ventral portion, with the exception of the flexor tubercle (which is convex and robust in form), is flattened across its length. Distinctive rugosities cover the ungual's surface, though they are most apparent on the posterior regions. Possibly due to erosion, these pits are shallower on the medial side of the bone than on the lateral one.

A deep groove extends from the dorsomedial margin of the flexor tubercle, terminating just posterior to the missing distal tip. At its inception, this groove is placed in the lower 1/3 of the dorso-ventral complex, a form maintained for 3/4 of the claw’s curvature. However, this placement rapidly migrates dorsally at the 3/4 point until it reaches the top 1/3 of the bone. The groove reaches its maximum width halfway through the claw’s total length. A similar groove can be found on the lateral side of the claw. However, this groove is much deeper, a feature that may also be in part due to erosion of the medial surface.The lateral groove differs substantially from the medial one in that it thins radically to a ‘crack-like’ form 3/4 of the way through the medial groove’s duration.

The flexor tubercle is large and robust, being subequal in width to the dorsal margin of the articular facet. Its form, whose posterior margin is placed anterior to the articular facet, is subtriangular in both posterior and ventral views.A deep, median ridge divides the articular facet, which is oval-shaped in posterior view. The ventral portion of this ridge is especially bulky, being twice as thick as the maximum width reached by the midline. The articular surface for the condyles of the penultimate phalanx is deeper on the medial side than its lateral counterpart. Given the overall proportions of the ungual and its articular surfaces, the phalanx to which it was connected in life was likely equally robust.

Friday, April 23, 2010

I want you to imagine for a moment that you are a wildlife photographer observing a waterhole in the Serengeti. The waterhole is positioned roughly 50 feet from the open plains. Much of the pool is surrounded by a thick belt of vegetation, with the exception of a 15 foot stretch of soft muddy shoreline. Given that this is the only water source in several miles, you tentatively assume that it would be a good place to capture photos of the various creatures native to the area.

As your luck would have it, after only a few minutes of waiting, a zebra approaches and, being wary of predators, approaches the hole for a drink. The zebra drinks its fill, and almost as quickly as he came, is gone. A moment later, another zebra approaches from the same direction, spends a short time drinking (from a spot 5 feet adjacent from the first zebra), and also departs the way he came (after all, it's easier to walk across the sandy beach than transverse through the thickets).

Then finally, just before you call the day to a successful close, a final zebra arrives for the much needed water, drinks what it needs, and walks away.

Looking at the tracks left behind by the animals, you begin to wonder: what would somebody who had only seen the traces they left while walking to and from the pool have thought? After all, these were animals that were roughly the same size, walking at roughly the same speed, spaced roughly equally from each other (4-5 feet between trackways), and all with similar goals/geographic restrictions. You know that they were three lone ungulates. You saw them yourself! But somebody, were they to visit this hole themselves would not have this information. It would be a reasonable conclusion that they walked in together.

Now, in this same thought experiment, transport yourself several millions of years into the future. The plains have long since gone, and the pool long dried. An observer (human or otherwise), while hiking through the now uplifted sediments derived from this pool sees these tracks. Unlike the previous viewer from the past, this person doesn't have access to the past geographic constraints. He doesn't know of the thick vegetation that proved to be such a limitation to the zebras. All he sees are three sets of tracks, each equally spaced, and formed by the same variety of foot, all walking in the same direction, turning in the same direction, and leaving.

He has several conclusions that he can make: either a. the track makers were walking in formation of a group of three, or b. there was a single track maker followed by two track makers (or vice versa). or c. there were three individual track makers, each of which either independently arrived at the waterhole at the same time and left at different times or arrived at different times and left at roughly the same time.

The point is: how can he possibly decide between these? Each scenario, though very different in life, would leave an identical trace. He may decide that they traveled as a group, or he may decide that they were individual creatures on their own schedules. The most he can accurately say is that it is possible that the track makers traveled as a group.

Of course, many more track makers over a much larger distance traveling for a much longer length of time would make the possibility of a group derived trackway more likely. But, like Schrödinger's cat, we won't be able to know without the possibility of doubt until we observe